Systemic lupus erythematosus (SLE) is an autoimmune disorder that affects approximately 322,000 people in the United States. The hallmark of this potentially fatal disorder is the production of autoantibodies, by autoreactive B-cells, against nuclear antigens. Currently, there is no cure for lupus and multiple B-cell targeted therapies have not been successful in clinical trials. The aim of this proposal is to study mechanisms of B-cell tolerance in the triple congenic (TC), Fas-sufficient, murine lupus background by means of the well characterized AM14 heavy chain transgenic mouse model. In this system, the AM14 rheumatoid factor (RF) binds exclusively to IgG2aa and not IgG2ab antibodies. Therefore, the AM14 system can be adapted to be in the presence or absence of the autoantigen. The first goal of the proposal is to characterize the activation of the RF AM14 B-cells in the TC background. Exogenous administration of autoantigen in young mice will be utilized to determine the role of the B-cell receptor, Toll-like receptors and non-specific factorsin the activation of the RF B-cells. The second goal will determine, through cell transfer experiments, whether the RF B-cells are anergized in the autoimmune and non-autoimmune backgrounds. In addition, the role of CD4 T-cells and TC-derived DCs in RF B-cell activation will be determined. Finally, the marginal zone and follicular distribution of the AM14 RF B-cells and its role in the breakdown of tolerance will be studied via histology and flow cytometry. A thorough understanding of B-cell tolerance and the breakdown that occurs in SLE will provide targets for future B-cell therapies.